Born in 1994, Hagino started swimming at 6 months of age and went on to break multiple age group records from an early age and set new records in junior high. As a 17-year old, he competed in his first Olympics Games in London, where he won a bronze medal in the 400m individual medley. In 2016 at the Rio Olympics he won gold in the 400m individual medley, silver in the 200m individual medley, and bronze in the 4x200m freestyle relay. From April 2017 he entered a 5-year partnership with Bridgestone and NIKE. He is aiming to earn multiple gold medals in Tokyo 2020.